A Differential Mobility Analyzer (DMA) System for Submicron Aerosol Measurements at Ambient Relative Humidity

A new differential mobility analyzer (DMA) system for measuring submicron aerosol size distribution at ambient relative humidity (RH), with special attention to implementation on aircraft, is described. The system includes an active RH controller, a cylindrical differential mobility analyzer (CDMA), and a condensation particle counter. A cascade controller consisting of 2 Proportional-Integral-Differential (PID) modules maintains the RH inside the CDMA at ambient RH. The flows are controlled with feedback PID controllers, which compensate for the variation of pressure as the aircraft changes altitude. This system was integrated into the CIRPAS Twin Otter aircraft and used to measure ambient size distributions during the ACE-Asia experiment, which was carried out from March to May 2001 in Japan